Windows lost nearly a full percentage point of market share for the second month in a row in December, pushing Microsoft’s operating system to a new low, an Internet measurement company reported on Friday.
Meanwhile, Apple’s Mac OS X posted a record gain that brought it close to a 10 per cent share for the first time since Net Applications began tracking operating system use.
In December, 88.7 percent of the people who browsed the Web sites that Net Applications monitors did so using machines powered by Windows, a 0.94 percentage point drop from November.
The slide was Windows' largest in the four years that Net Applications has collected operating system data, and the second record-setting monthly loss in a row for Microsoft's software.
During November, Windows' market share slipped 0.84 percentage point, dropping the operating system under 90 percent for the first time since Net Applications has been tracking OS use.
The combined decline of November and December totalled 1.8 percentage points, Windows' biggest two-month dip ever, nearly double that of its previous record, a 0.92 percentage point fall in December 2007 and January 2008.
Microsoft's OS ended the year down 3.1 percentage points, a 3.4 per cent drop in its share from the same time last year.
Apple's Mac OS X's market share continued to grow at Windows' expense. For the second month in a row, Mac OS X posted a record increase, growing by 0.76 of a percentage point to end the month at 9.6 per cent.
December was the first time that Net Applications had pegged Apple's operating system above the 9 per cent mark.
And just as Windows set a record for a two-month drop, Mac OS X set a record for a two-month increase during November and December.
Those months' combined gain of 1.4 percentage points was substantially larger than the earlier record, a 0.9 percentage point boost the operating system received in September-October 2006, and almost double the 0.73 percentage point increase of November-December 2007.
Mac OS X's market share was up 2.3 percentage points during 2008, an annual growth rate of 31.7 per cent .
Net Applications again attributed some of the decline of Windows and the corresponding growth of Mac OS X to special circumstances.
"The December holiday season strongly favoured residential over business usage," the company said on its Web site. "This in turn increases the relative usage share of Mac...and other products that have relatively high residential usage. All December usage statistics should be read in that context."
Last month, Net Applications' executive vice president of marketing, Vince Vizzaccarro, said November's drop in Windows share was due to the higher-than-average number of weekend days and the Thanksgiving holiday in the US Net Applications has consistently reported that Windows' share slips during times when browsing is conducted from non-work computers, where Microsoft's operating system dominates even more than in homes.
Even so, Windows' market share fall for November-December 2008 was more than twice that of any similar period in the preceding three years. During the same two months of 2007, for example, Windows lost 0.7 of a percentage point, while in 2006 and 2005, Microsoft's operating system dropped 0.45 of a percentage point and 0.51 of a percentage point, respectively.
As has been the case throughout most of the year, Windows XP accounted for the bulk of Microsoft's downturn. During December, the seven-year-old operating system lost 1.1 percentage points.
Windows Vista 's share, on the other hand, increased slightly to finish the year just above 21 per cent.
Net Applications' operating system market share numbers can be found on the company's Web site.